PURPOSE: To increase the extraction quantity of the liquid N2 by sucking the outlet gas of an expansion turbine by a load blower to increase the differential pressure between the inlet gas and the outlet gas of the expansion turbine and increase the cold.

CONSTITUTION: The exhaust gas is introduced as the inlet gas of an expansion turbine 4 by an extraction pipe 67, and the expansion turbine 4 is operated by the exhaust gas. Because a load blower 41 is also operated by this operation, the outlet gas of the expansion turbine 4 is sucked into the load blower 41 through a main heat exchanger and an exhaust pipe 60, and as a result, the outlet gas of the expansion turbine 4 is dropped in pressure. The outlet gas of the expansion turbine 4 is dropped in pressure through the adiabatic expansion at the expansion turbine 4, and also dropped in pressure through the suction at the load blower 41. The differential pressure between the inlet gas and the outlet gas at the expansion turbine 4 is larger than that in a case of only the pressure drop caused through the adiabatic expansion at the expansion turbine 4 in a conventional nitrogen manufacturing device, and the cold is also increased, and the extraction quantity of the liquid N2 can be increased.